Is Nunu (and Willump) broken?

I'm hesitant to write this because I'm probably one of the few people seemingly dumb enough to play Nunu in top lane (I don't play jungle) and I'm a low-elo player (Gold V). However, I'm pretty sure that Nunu has been overbuffed to the point that he's arguably unhealthy for the meta. Nunu's sustain is stupid, he can afford to make dumb trades and just Q the enemy top laner or a minion after and auto-win the trade (it's very difficult for the enemy top laner to play aggro against Nunu). His W makes for stupidly easy follow-ups on ganks and also allows for easy roaming potential. His E feels like possibly the weakest part of his kit but being able to hit through minions and then root afterwards is pretty strong, and with his W and R, it creates pretty solid CC lockdown. I don't really have any problems with his ult since it's fairly easy to disrupt, though the shield and damage are still pretty damn strong (plenty of times I've just rolled up to an ADC and pressed R to kill them).

So far I've been playing him as an AP bruiser top (RoA, Liandry's, etc.) with Aftershock and despite the pretty bad waveclear and AP bruiser probably not being the best build, Nunu can still make an overwhelmingly big impact. I'm guessing part of the reason he feels so strong right now is because he seems to do pretty well against a number of bruisers with his heavy CC and pretty solid damage, though there are still a fair few champs that seem to do well against him (Viktor, Camille, Riven?), but right now I feel like he is a bit overtuned (the small AD buff was nice though). Hell, he can fairly comfortably solo Baron without even being that close to full build (albeit pretty slowly though the Q still does 980 true damage every 8 seconds with 0% CDR).

Can anyone back me up on this?

P.S. I don't think a lot of people realise how stupidly mobile Nunu is with his snowball if you pull the cursor to the side hard enough (I didn't realise for weeks), probably because they didn't move their mouse enough to keep up (keep the cursor 90 degrees to the side of Nunu and he practically turns on a dime, the snowball even flickers to change angle because it can't keep up).